If an object weighed one pound on the surface of the earth, how much would it weigh 4,000 miles above the earth?

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问题 If an object weighed one pound on the surface of the earth, how much would it weigh 4,000 miles above the earth?
Because we can feel that things are heavy, we think of weight as being a fixed quality in an object, but it is not really fixed at all. [18]If you could take a one pound packet of butter 4,000 miles out from the earth, it would weigh only a quarter of a pound. Why would things weigh only a quarter as much as they do at the surface of the earth if we took them 4,000 miles out into space? [19]The reason is this: All objects have a natural attraction for all other objects; this is called gravitational attraction, but this power of attraction between two objects gets weaker as they get farther apart. When the butter was at the surface of the earth, [20]it was 4,000 miles from the centre, in other words the radius of the earth is 4,000 miles. When we took the butter 4,000 miles out, it was 8,000 miles from the centre, which is twice the distance. If you double the distance between two objects, their gravitational attraction decreases four times weaker. If you treble the distance, it gets nine times weaker. If you take it four times as far away, it gets sixteen times weaker and so on.

选项 A、3/4 pounds.
B、4 pounds.
C、1/9 pound.
D、1/4 pounds.

答案D

解析 短文开头举例说,把一磅重的黄油带到地球4000英里外就只有a quarter重,明白a quarter即1/4,就不难选出答案为D。
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